### Please describe the problem.

git annex multicast --send quits with error "Invalid keytype"


### What steps will reproduce the problem?

Follow the example in the multicast command help page, the send operation fails when uftp version is 5.0.

Probably the reason is the removal of aes256-cbc in version 5.0 where they left aes256-gcm

### What version of git-annex are you using? On what operating system?

git-annex version: 8.20211028
OS is nixos-21.11 with uftp installed
uftp 5.0

### Operation log

[[!format sh """
# If you can, paste a complete transcript of the problem occurring here.
# If the problem is with the git-annex assistant, paste in .git/annex/daemon.log
$ git annex multicast --send --debug
sending files [2022-04-17 00:15:46.699593866] (Utility.Process) process [60540] read: git ["--git-dir=.git","--work-tree=.","--literal-pathspecs","-c","annex.debug=true","symbolic-ref","-q","HEAD"]
[2022-04-17 00:15:46.701266922] (Utility.Process) process [60540] done ExitSuccess
[2022-04-17 00:15:46.701754626] (Utility.Process) process [60541] read: git ["--git-dir=.git","--work-tree=.","--literal-pathspecs","-c","annex.debug=true","show-ref","refs/heads/master"]
[2022-04-17 00:15:46.703889652] (Utility.Process) process [60541] done ExitSuccess
[2022-04-17 00:15:46.70436486] (Utility.Process) process [60542] read: git ["--git-dir=.git","--work-tree=.","--literal-pathspecs","-c","annex.debug=true","ls-files","-z","--cached","--"]
[2022-04-17 00:15:46.706736386] (Utility.Process) process [60543] chat: git ["--git-dir=.git","--work-tree=.","--literal-pathspecs","-c","annex.debug=true","cat-file","--batch-check=%(objectname) %(objecttype) %(objectsize)"]
[2022-04-17 00:15:46.709237395] (Utility.Process) process [60544] chat: git ["--git-dir=.git","--work-tree=.","--literal-pathspecs","-c","annex.debug=true","cat-file","--batch"]
[2022-04-17 00:15:46.729027634] (Utility.Process) process [60542] done ExitSuccess
[2022-04-17 00:15:46.729292044] (Utility.Process) process [60545] read: git ["--git-dir=.git","--work-tree=.","--literal-pathspecs","-c","annex.debug=true","show-ref","git-annex"]
[2022-04-17 00:15:46.730468539] (Utility.Process) process [60545] done ExitSuccess
[2022-04-17 00:15:46.730735082] (Utility.Process) process [60546] read: git ["--git-dir=.git","--work-tree=.","--literal-pathspecs","-c","annex.debug=true","show-ref","--hash","refs/heads/git-annex"]
[2022-04-17 00:15:46.73204795] (Utility.Process) process [60546] done ExitSuccess
[2022-04-17 00:15:46.732421746] (Utility.Process) process [60547] read: git ["--git-dir=.git","--work-tree=.","--literal-pathspecs","-c","annex.debug=true","log","refs/heads/git-annex..fd32a06095805399cdaf708cd294158b8d05027b","--pretty=%H","-n1"]
[2022-04-17 00:15:46.733706532] (Utility.Process) process [60547] done ExitSuccess
[2022-04-17 00:15:46.735507734] (Utility.Process) process [60548] chat: git ["--git-dir=.git","--work-tree=.","--literal-pathspecs","-c","annex.debug=true","cat-file","--batch"]
[2022-04-17 00:15:46.737226695] (Utility.Process) process [60549] call: uftp ["-c","-Y","aes256-cbc","-h","sha512","-e","ecdh_ecdsa","-k",".git/annex/creds/multicast","-U","0x1de1f677","-H","@/tmp/authlist60534-1","-i","/tmp/send60534-0"]
Invalid keytype
[2022-04-17 00:15:46.748492634] (Utility.Process) process [60549] done ExitFailure 1
failed
ok


# End of transcript or log.
"""]]

### Have you had any luck using git-annex before? (Sometimes we get tired of reading bug reports all day and a lil' positive end note does wonders)

Of course! I'm using it to track assets in an infrastructure repository

> I've changed it to use aes256-gcm. I have not verified if there
> is other breakage from the new version, so file a bug if you find any.
> [[done]] --[[Joey]]
